Duane Schaub <[EMAIL PROTECTED]> wrote:
>
> I want to set up multiple qmail machines to access an NFS backend. We have
> about 10,000 users (running maildir) and an average of 5 emails/user/dat and
> av. 10K in size.
50,000 messages a day, 10k each? Not a huge load. We handle about a tenth of
that on one machine with a P733 and SCSI disks. System load is typically <<
0.1 (i.e., negligible).
> On average, there are 6 simultaneous pop sessions with approx. 200 new
> sessions/min.
This could be the big problem.
> We have tried a Redhat6.1 backend on the NFS with Redhat 6.1 NFS clients.
You're not using the default kernel shipped with RH6.1, are you? That would
be 2.2.5-something. Early 2.2 kernels are known to have absolutely terrible
NFS performance as NFS servers, and client-side isn't a whole lot better. NFS
has gotten somewhat better in 2.2.19, but server-side is still not up to
snuff. You may want to run OpenBSD or FreeBSD as the NFS server.
> The NFS server was nothing special (P350/IDE 256Mb RAM).
This is your biggest problem. This is not a performance workstation class
machine, let alone a high-performance server. You'll notice a huge difference
just in switching to SCSI with Linux, even cheap 7200rpm SCSI disks on an
average controller. For your load, I would recommend good 15kRPM SCSI disks
in a hardware RAID setup (not software RAID). This would probably cure your
performance issues on the NFS server. Adding additional RAM would likely
benefit as well, as more of the filesystem could be cached. Memory is so
cheap these days that you might want to jump right to 1GB.
> The result was that the qmail machines were BARELY able to keep up. If
> there were any pauses on the NFS server, the POP sessions would build to
> 50-60 very quickly with qmail crashing at about 300 sessions.
If qmail is "crashing" (prove it!) due to POP3 load, you've seriously
misconfigured your server. You should be using tcpserver's concurrency limits
to enforce a maximum limit on concurrent POP3 connections to a level that your
system can actually handle. qmail itself doesn't crash for any reason related
to POP3 access.
> If you wish - respond privately [EMAIL PROTECTED]
No, I think I'll keep it on the list. That way others can benefit from your
experiences and learn from them, rather than asking the same question next
week, next month, next year...
Charles
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Charles Cazabon <[EMAIL PROTECTED]>
GPL'ed software available at: http://www.qcc.sk.ca/~charlesc/software/
Any opinions expressed are just that -- my opinions.
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